Skeletal Muscle Metabolism of Sea-Level Natives Following Short-Term High-Altitude Residence,
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA
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The influence of short-term high-altitude HA residence on intramuscular pH and skeletal muscle enzyme activity of sea-level SL residents was investigated. Vastus lateralis muscle samples were obtained by biopsy from rested subjects n-5 at SL 50M and on the eighteenth day of HA residence 4300 m for determination of glycogen phosphorylase, hexokinase, malate dehydrogenase and total lactate dehydrogenase activities. A second group of subjects n-6 performed cycle exercise of the same absolute intensity at SL and on the fifteenth day of residence at HA. The first group of subjects showed no significant changes in skeletal muscle enzyme activity laser after 18 days at HA. The second group of subjects were instructed to exercise for exactly 30 min, and all but one could complete the entire bout at SL. However, at HA, none could continue 30 min, and time to exhaustion was 11.9 or - 1.6 min. Resting intramuscular pH was not significantly different after HA residence as compared to SL. The fall in intramuscular pH was less with exercise on day 15 at HA than during SL exercise. Likewise, the increase in blood lactate concentration with exercise at HA was less than at SL. These data indicate that, after 15-18 days of HA residence, limitations in exercise performance are not due to inordinate intramuscular acidosis or to changes in the activity of glycolytic and oxidative enzymes.
- Stress Physiology